This invention relates generally to remote object position and orientation determining systems employing an electromagnetic coupling and more particularly is directed to new processing techniques for such systems.
Remote object position and orientation determining systems employing electromagnetic couplings are known in the prior art. Such systems are used for tracking and determining the position and orientation of remote objects in a wide variety of applications. Such systems traditionally have a source assembly that includes a set, typically three, generally concentrically positioned, of orthogonal field-generation antennas for generating a plurality of electromagnetic fields. Located at the remote object is a sensor having a set, also typically three, generally concentrically positioned, of orthogonal receiving antennas for receiving the electromagnetic fields generated by the transmitting antennas and producing signals corresponding to the received electromagnetic fields.
Processing algorithms for resolving the signals produced by the receiving antennas into remote object position and orientation contain implicit assumptions that the field-generation antennas are spherically concentrically positioned (meaning that their center be collocated) and that the receiving antennas are spherically concentrically positioned. These assumptions may not be warranted depending on manufacturing tolerances and on desired accuracy. Because of the manner in which coils are wound and because of practical tolerances of collocating the coils' centers or the centers of other types of magnetic field antennas, the three antennas' centers can be displaced from an intended common center by appreciable amounts. Because each field measurement data interpreted by the processing algorithm is the result of two operating coils, a source coil and a sensor coil, both of which may be experiencing non-concentricity, the opportunity for error in the position and orientation solution is very great.
Early remote sensor tracking systems, which operated within a relatively small volume of space with relatively limited sensor attitude angles, did not require exceptional accuracy. With such low performance expectations, manufacturing techniques were sufficient to keep non-concentricity deficiencies of the source and sensor within acceptable tolerances. As accuracy requirements have become more demanding and other sources of error have been eliminated or mitigated in position and orientation measurement systems, errors resulting from source and sensor non-concentricity have become a limitation of system accuracy performance. Attempts at solving non-concentricity errors by better manufacturing processes have not only proved to be ineffective but have added significant cost.
Prior art position and orientation algorithms have dictated a requirement that the centers of the coils in the coil set making up the source antennas be collocated and the centers of the coils of the coil set making up the sensor antennas be collocated. In addition to the difficulty of accurately manufacturing such devices, this places a severe constraint on source and sensor coil configuration. Other coil geometries may produce more desirable packaging.